Medical balloons can be deflated and inflated about their long supporting devices and placed in bodily conduits to administer treatments, for example, deployment of stents or widening of constricted passages during angioplasty, valvuloplasty, or urological procedures.
In angioplasty, for example, coronary angioplasty, a balloon can be used to treat a stenosis by collapsing the balloon and placing it in a bodily conduit, e.g., a coronary artery. The balloon is then inflated, e.g., by injecting a fluid, at a region of the artery that has been narrowed to such a degree that blood flow is restricted. Inflating the balloon can expand the stenosis radially so that the vessel will permit an acceptable rate of blood flow. This procedure can be a successful alternative, for example, to coronary arterial bypass surgery. After use, the balloon is deflated or collapsed and withdrawn.
Medical balloons can be manufactured by extruding a cylindrical tube of polymer and then pressurizing the tube while heating to expand the tube into the shape of a balloon. The balloon can be fastened around the exterior of a hollow catheter shaft to form a balloon catheter. The hollow interior of the balloon is in fluid communication with the hollow interior of the shaft. The shaft may be used to provide a fluid supply for inflating the balloon or a vacuum for deflating the balloon.
It is important that the balloon have a generally predictable shape on inflation. Typically, the balloon, such as a regular balloon, should have proximal and distal taper regions with closely matched taper angles and a uniformly cylindrical dilatation region. A deformed regular balloon, however, may have an irregular profile, such as a taper extending along the length of the dilatation region or portions with non-uniform cross sectional diameters. As a result, during use, deformed regular balloons may undesirably provide unpredictable, and thus unreliable, inflations/deflations or stent deployments. It is believed that deformed balloon shapes can be caused by locking the polymeric chains in undesirable configurations during manufacture, referred to as polymeric stress. The release or partial release of this stress, e.g., during heat sterilization, can also cause deformation.